In packaging industry, the welding and cutting of polymeric sheets is a very important issue. Polymeric materials are used to make all kinds of packages and in the case of food industry these packages can be for example pouches that contain liquid such as milk or sealed bags that contain solid food. For the food industry is it a requirement to have a packaging process that is reliable, of very high quality, and hygienic. Furthermore, the packaging process should be fast, efficient and easy to control.
In the industry of form/fill/seal packaging at high speed, conventional machines fall into two distinct categories, namely continuous and intermittent motion machines. In continuous motion machines, the packages are formed and sealed at a fixed speed and in intermittent motion machines, the package is momentarily immobilized at a cutting station for the time duration of the sealing process. Form/fill/seal packaging machines that are used to produce milk pouches are intermittent motion machines that can form/fill/seal milk pouches with typically a high rate of more than 1 liter per second. These machines use a heating system to seal and cut, in one operation step, the polymeric films therefore forming a bag or a pouch. Heating the polymeric films locally has the effect to weld the films together creating simultaneously two seals region separated by a region where the films are cut. The process must be well-controlled since too much heat can damage the integrity of the films whereas not enough heat will poorly weld the films.
In the industry of form/fill/seal packaging at high speed, the sealing systems that are generally in use utilize an electrical resistance wire that is heated by an electrical pulse. The heated wire is brought into contact with the films where the films are aimed to be sealed and cut, and the heat of the wire is transferred partially to the films therefore creating the seal. An example of this kind of machine can be found in U.S. Pat. No. 6,237,308 B1. Although this system allows for high speed packaging and is a well-mastered process, it has some drawbacks. The first drawback of this system is that the hot wire must be in contact (directly or indirectly via a disposable release sheet) with the films to transfer the heat to the films. This can lead to contamination problems and the hot wire and/or the release sheet must often be changed. The actual technique is also not a very efficient process since the film area that is heated via this process is much larger than what is really needed to make the seal. Finally, since the hot wire is located in a mechanical clamp that brings the films into contact, it is subject to mechanical vibrations that can affect the seal quality.
The use of lasers to seal and cut polymeric films in a continuous sealing apparatus is known from U.S. Pat. No. 6,207,925 B1. Three laser beams are controlled to perform the transverse seal-cut-seal action between two contiguous packages. Each laser is devoted to either seal or cut the films. Because of the continuous motion of the films, the time for the laser beams to perform the cut and seal is extended substantially to the whole package cycle. The teachings of U.S. Pat. No. 6,207,925 B1 cannot be readily adapted for use with intermittent motion form/fill/seal machines and the spot beam precision control in the case of continuous motion machines remains costly.
Therefore there is a need for a method and an apparatus for improving the sealing and cutting process of a high speed packaging machine, in order to increase the efficiency of the process, to reduce the mechanical contact between the heating source and the films, and to increase the overall lifetime of the machine components.